The invention pertains to a windshield wiper unit which is used especially for motor vehicles.
More specifically the invention pertains to a windshield wiper having a wiper arm of telescopic construction which has a housing driven by a driving motor to an fro about an axis of rotation. Such a wiper arm has a slide movable in relation to the housing. The slide is supported in two bearings in the housing spaced apart from each other and has a length at least equal to the distance between the bearing plus the stroke. The displacement is achieved via a connecting rod linked to the slide and a crank linked to the connecting rod. The crank has a fixed axis of rotation relative to the housing and is driven by a gear.
Such a windshield wiper unit is known from DE-PS 31 25 628. In this unit the slide, which is normally movable in a radial direction in relation to the axis of rotation of the driven housing, is supported in two friction bearings of the housing. The distance between the bearings is about two-thirds of the length of the slide. The axis of rotation of the housing is comparable with the axis of the wiper shaft of an ordinary windshield wiper unit without an extendable wiper arm. The friction bearing which is nearest to the axis of rotation will be referred to hereinafter as the rear bearing and the other friction bearing will be referred to as the front bearing.
Linked to the rear end of the slide is a connecting rod which is furthermore linked to a crank. The axis of rotation of the crank coincides with the axis of rotation of the driven housing. The axis of rotation of the crank is therefore simultaneously fixed in relation to the vehicle and in relation to the housing. The crank is unrotatably connected with a gear wheel. The gear wheel is driven, via a pinion with an axle which is fixed in relation to the vehicle by an internal gear ring of the housing which moves to and fro. The center axis of the internal gear ring coincides with the axis of rotation of the housing.
It is not absolutely necessary for the axis of rotation of the crank to be identical with the axis of rotation of the housing which moves to and fro. As shown by DE-OS 22 15 307, a gear ring whose axis of rotation coincides with the axis of rotation of the housing which moves to and fro is arranged so as to be fixed in relation to the vehicle, while the axis of rotation of the crank and of the gear wheel non-rotatably connected with it is outside the axis of rotation of the housing and fixed only in relation to the housing. With this design, too, it is simplest if the axis of rotation of the crank runs parallel to the axis of rotation of the housing and intersects a straight line determined by the longitudinal direction of the slide.
In the known windshield wiper systems, the unit consisting of the slide and the drive of the slide is altogether very long. Furthermore, there is a relatively heavy load on the bearings.